New synthesis of 2,6-anhydro-β-d-fructofuranoses, pivotal [2.2.1] bicyclic acetals for the conversion of d-fructose into 2,2,5-trisubstituted tetrahydrofurans

Effect of conformational rigidity on the stereoselectivity of nucleophilic additions to five-membered ring bicyclic oxocarbenium ion intermediates

“…The reaction mixture was concentrated in vacuo, and the product was purified by flash column chromatography on silica gel (25 : 75 EtOAchexanes) to give 12 as a colorless oil (0.065 g, 94%). Characterization was performed on a 50 : 50 mixture of diastereomers: 1 H NMR (600 MHz, CDCl 3 ) δ 5.48-5.45 (m, 1H), 4.16 (dt, J = 10.0, 7.9, 0.5H), 4.01 (ddd, J = 10.7, 8.4, 5.2, 0.5H), 3.89-3.84 (m, 1H), 3.82-3.71 (m, 2H), 3.03 (br s, 1H), 2.62 (ddd, J = 14.1, 8.8, 5.8, 0.5H), 2.23-2.14 (m, 1.5H), 2.06 (ddd, J = 12.4, 10.3, 5.5, 0.5H), 1.87-1.74 (m, 3.5H), 1.71-1.62 (m, 1H), 1.51 (dddd, J = 12.9, 11.0, 8.5, 6.1, 0.5H), 1.40 (dddd, J = 13.1, 10.7, 8.8, 5.7, 0.5H); 13 (5). To a solution of 12 (0.020 g, 0.13 mmol) in CH 2 Cl 2 (1 mL) at 0 °C was added triethylamine (0.106 mL, 0.759 mmol) and acetic anhydride (0.024 mL, 0.25 mmol).…”

“…These reactions are useful in natural product synthesis 1,2 and can be used to control stereochemistry at tetrasubstituted carbon stereocenters. [3][4][5][6] These reactions, many of which proceed through oxocarbenium ion intermediates, are also important in carbohydrate 7 and nucleoside chemistry, 8,9 including the synthesis of non-natural nucleosides. 10 Our laboratory 11,12 and others [13][14][15][16] have explored the origin of stereoselectivity in reactions of five-membered ring oxocarbenium ions.…”

Recent Advances in the Chemical Synthesis of C-Glycosides

“…10,751,752 TiCl 4 -mediated reaction of 2,7-dioxabicyclo[2.2.1]heptane 808 with allyltributylstannnane gave 2,5-trans-disubstituted tetrahydrofuran 809 as the predominant product (trans/cis = 93:7) in 84% yield (Scheme 134). 753,754 C-Allylation of 1,2-O-isopropylidene furanose derivative 810 with allyltrimethylsilane under the promotion BF 3 •OEt 2 probably proceeded through the inside attack of the stable oxocarbenium ion intermediate A, affording C-furanoside 811 with high 1,3-trans stereoselectivity in 65% yield (Scheme 134). 755,756 Recently, the PPh 3 AuNTf 2 -catalyzed C-glycosylation of the glucosyl, 2-deoxyglucosyl, and 2-deoxyribofuranosyl orthoalkynylbenzoates with allylsilane was reported to provide Cglycosides 348, 812, and 813 in high yields (>80%) with the αanomers as the only or predomiant products (Scheme 135).…”

“… ,, TiCl 4 -mediated reaction of 2,7-dioxabicyclo[2.2.1]­heptane 808 with allyltributylstannnane gave 2,5- trans -disubstituted tetrahydrofuran 809 as the predominant product ( trans / cis = 93:7) in 84% yield (Scheme ). , C -Allylation of 1,2- O -isopropylidene furanose derivative 810 with allyltrimethylsilane under the promotion BF 3 ·OEt 2 probably proceeded through the inside attack of the stable oxocarbenium ion intermediate A , affording C -furanoside 811 with high 1,3- trans stereoselectivity in 65% yield (Scheme ). , …”

Nucleophilic Ring‐Opening of 1,6‐Anhydrosugars: Recent Advances and Applications in Organic Synthesis

“…The Lewis acid‐mediated ring‐opening of [2.2.1] bicyclic acetals, that may be seen as constrained analogues of 1,6‐anhydrosugars, has been also studied (Scheme 7). [23] The reaction of 2,6‐anhydro‐β‐D‐fructofuranoses with allyltrimethylsilane in the presence of 10 mol% of Sc(OTf) 3 afforded the expected bis‐C ‐glycosides [23a,24] in good yields with complete regioselectivity. 2,2‐Disubstituted tetrahydrofurans are found in many compounds of biological interest including syringolide, secosyrin, and sphydrofuran natural products [25] .…”